The invention is generally directed to uncoated papers, and more specifically, the present invention is directed to economical twin ply papers useful in ink jet processes. Thus, in one embodiment the present invention relates to uncoated twin ply papers containing, for example, various liquid absorbing fillers, inclusive of specific silicas, which papers enable the rapid absorption drying of ink jet compositions, and wherein the images obtained are comparable to silica coated grade ink jet papers, and are of superior image quality as compared to the ordinary uncoated papers, as illustrated in M. Lyne and J. S. Aspler, "Paper for Ink Jet Printing", TAPPI Journal 68 (5) 1985, pp. 106-110. Also, the twin ply papers of the present invention exhibit improved drying in that, for example, no heating is needed as is the situation with some coated and uncoated papers presently selected for ink jet processes. In addition, the uncoated twin-ply papers of the present invention have substantially no undesirable show-through and strike-through characteristics, and images generated thereon are of improved sharpness, that is for example there is negligible image raggedness as compared to many known uncoated and coated ink jet papers. Furthermore, the uncoated papers of the present invention are similar to ordinary paper in feel, appearance and receptiveness to lead pencil marking, while simultaneously possessing printing performances comparable to premium grade ink jet coated papers. Additionally, the twin ply papers of the present invention are also useful in other liquid development systems, such as electrostatic xerography and direct electrography.
Pigment coated papers developed for ink jet processes are well known. These papers are usually comprised of a supporting substrate and thereover high surface area hydrophilic pigment, such as colloidal silicas dispersed in an appropriate organic binder system. Disadvantages associated with these papers, especially the coating thereof, include their high process costs, relatively poor substrate adhesion, and the need for special coating processes to circumvent the peculiar rheology associated with the high surface area pigments selected. Additionally, the prior art coated papers do not have the feel, appearance and pencil marking receptivity of ordinary paper, and therefore are undesirable to some users.
As indicated herein, the uncoated papers of the present invention are especially useful in ink jet processes. Marking compositions which are useful in the aforementioned ink jet printing processes are well known, and generally contain water soluble dyes. There is thus described, for example, in U.S. Pat. No. 3,846,141, the disclosure of which is totally incorporated herein by reference, an ink composition useful in jet printing comprised of an aqueous solution of a water-soluble dye and a humectant material formed of a mixture of a lower alkoxy triglycol; and at least one other compound selected from the group consisting of a polyethylene glycol, a lower alkyl ether of diethylene glycol, and glycerol. According to the disclosure of this patent, the printing inks have the desired viscosity for use in jet printing in that the viscosity of the composition is subjected to little variation with use as water is lost by evaporation during recirculation of the ink composition through the jet printer. Further, apparently the humectant system disclosed in this patent substantially prevents or minimizes drying of the printing ink in the orifice or nozzle during down time of the printer, such as when the printer is rendered inoperative. As further disclosed in this patent, the basic imaging technique in ink jet printing involves the use of one or more ink jet assemblies connected to a pressurized source of ink. Each individual ink jet includes a very small orifice usually of a diameter of 50 microns, which is energized by magneto restrictive piezo-electric means for the purpose of emitting a continuous stream of uniform droplets of ink at a rate of 33 to 75 kilohertz. This stream of droplets is then directed onto the surface of a moving web of, for example paper, and is controlled to form printed characters in response to video signals derived from an electronics character generator, and as a result of an electrostatic deflection system. In addition, there are disclosed in U.S. Pat. No. 4,279,653 ink jet compositions containing water-soluble wetting agents, a water-soluble dye and an oxygen absorber. Similarly, U.S. Pat. No. 4,196,007 describes an ink jet printing composition containing an aqueous solution of a water-soluble dye and a humectant consisting of at least one water-soluble unsaturated compound. Other prior art disclosing aqueous inks for ink jet printing include U.S. Pat. Nos. 4,101,329; 4,290,072; 4,383,859; 4,235,773; 4,279,814; 4,443,371; 4,286,989 and 4,299,630. Additionally, there is disclosed in U.S. Pat. No. 4,197,135 ink compositions with improved waterfastness comprised of at least one water soluble dye, and a polyamine with 7 or more nitrogen atoms per molecule. The disclosures of each of the aforementioned patents are totally incorporated herein by reference.
Therefore, there is a need for uncoated papers that are useful in ink jet processes. In addition, there is a need for economical uncoated ink jet papers providing image performance comparable to silica coated papers; and further the papers of the present invention have the feel and appearance of ordinary uncoated paper. Additionally, there is a need for uncoated papers that will enable the rapid drying of inks on the surface thereof, which papers also permit developed images of high resolution, and superior density when compared, for example, to many prior art papers.